It is proposed to continue studies of the morphology, organization, synaptic connections and immunochemistry of neurons in the visual cortices of rat, cat, and monkey. A Golgi-EM technique will be employed to examine the morphology and synaptic connections of neurogliaform cells, local circuit neurons, and pyramidal cells. The results of such studies will be correlated with data obtained using antibodies to putative and potential neurotransmitters to determine the distribution of chemically defined groups of neurons and their terminals. It is also proposed to develop techniques for using combinations of antibodies, and antibodies plus Golgi-EM to determine how differentially labeled neurons interact. Although it has long been held that there are only two morphological types of synapses in cerebral cortex, this view is questioned, for there are certainly more than two types of axon terminals which can be distinguished on the basis of the sizes of their synaptic vesicles. It is intended to ascertain how many types of axon terminals and synapses really exist, how they are distributed, and if correlations can be made between the sources of the terminals, their morphology and their transmitter content. Finally, rat visual cortex will be used to determine if it contains regularly arranged groups of vertically oriented neurons, which give the cortex a patterned matrix. The goal is to better define how cortical neurons normally interact, for until this is understood it is not possible to appreciate the changes which occur in altered states, and how neuronal function can be altered by drugs.